1. Field of the Invention
The present invention relates to a stepping motor for performing rotational movement corresponding to pulse power, in particular, in which a magnet and yokes are axially arranged and one ends of the yokes are so provided to surround a portion of the magnet, thereby enabling downsizing of the stepping motor while ensuring stable driving characteristics thereof.
2. Description of the Related Art
In general, a stepping motor maintains a very large static torque in the stopped position compared to other motors while being rotated at a given angle without feedback for detecting the position of a shaft and stopping at a considerably high precision rate. Therefore, the stepping motor does not require a separate position-maintaining mechanism such as electromagnetic brake and the rotation speed thereof is proportional to pulse rate, and thus the stepping motor has a driving characteristic that it can be readily controlled.
Due to such characteristics, the stepping motor is generally used in operations for precisely controlling mechanical movement, and in particular, widely used as a driving source of since it can be controlled digitally via pulse.
For example, the stepping motor is used as a driving source for controlling the printing position of a print head, the pen position of an X-Y plotter or the head position of a floppy disk and various disk ROMs. Also, the stepping motor is used for precision control of various electronic instruments such as paper money counter, sewing machine, electric typewriter and facsimile.
FIG. 1 is a schematic sectional view showing a stepping motor of the prior art, and FIG. 2 is a perspective view showing the stepping motor of the prior art. As shown in the drawings, the stepping motor is mainly comprised of a rotor and a stator.
The rotor is constituted of a shaft s and a magnet m. The shaft s functioning as an output end having a predetermined length is inserted into bearings b coupled in central planes of the first and second cover plates c1 and c2 to be supported rotationally in a forward or reverse direction. In the outer circumferential face of one end of the shaft s, is provided the magnet m substantially shaped as a cylinder, which has a configuration that N and S poles are alternately magnetized in the outer circumferential face.
Meanwhile, the magnet m is arranged opposite to the following coils 130 and 230 in the inner circumferential face of the stator with a predetermined air gap therefrom to generate a predetermined amount of electromagnetic force through the interaction.
The stator is mainly comprised of the first and second stators 100 and 200 in the shape of a cylinder. The stators 100 and 200 are arranged and coupled colinear, and provided in the inner faces with the first and second yokes 110 and 210 around which the coils 130 and 230 are wound.
In particular, the first yoke 110 has an inside bobbin 120 and the coil 130 wound around the outer face of the bobbin 120. In the inner face of the rotor opposed to the magnet m, the yoke is alternately arranged to have a shape of tooth-type engagement.
The second yoke 210, as the first yoke 110, is provided in the inner face with a bobbin 220 around which the coil 230 is wound. In the inner face of the foregoing rotor opposed to the magnet m, the yoke is alternately arranged to have a shape of tooth-type engagement.
Meanwhile, the first and second stators 100 and 200, when seen from the drawings, are so configured that the right and left faces are integrally fixed by the first and second cover plates c1 and c2 interposing bearings in the central face for rotationally supporting the shaft s.
In the conventional stepping motor having the configuration as set forth above, when both of the coils 130 and 230 of the first and second stators 100 and 200 are externally applied with current, the coils 130 and 230, the first and second yokes 110 and 210 and the magnetic poles of the magnet m undergo interaction to generate electromagnetic force, thereby causing the rotor having the magnet m and the shaft s to rotate about the first and second stators 100 and 200.
Lately, as the precision instruments are downsized and thin-shaped, the stepping motor mounted to the precision instruments is also required to be slimmed. However, the conventional stepping motor comprises a number of components having diameters different from each other in the outer circumferential face about the shaft s, thereby restricting downsizing.
For example, there is a method for downsizing the conventional stepping motor by reducing the diameters of the magnet m and the coils 130 and 230. In this configuration, however, electromagnetic force of the magnet m and the coils 130 and 230 are lowered also, thereby lowering mutual electromagnetic force by a large margin. Therefore, as the motor is downsized, the output capacity is also lowered thereby restricting downsizing.
The present invention has been devised to solve the foregoing problems and it is therefore an object of the invention to provide a stepping motor in which a magnet and yokes are axially arranged and one end of the yokes is provided to surround a portion of the magnet, thereby enabling downsizing of the stepping motor while ensuring driving characteristics thereof.
In accordance with an aspect of the invention to obtain the foregoing object, a stepping motor comprises: a rotor having a cylindrical magnet with a plurality of N-S poles being radially magnetized thereto and a shaft having one end coupled to the center of the magnet and rotationally supported by bearings; at least one coil wound into the shape of a ring at axial sides of the magnet with air gaps; and a stator shaped as a cylinder with a shaft hole in the center for receiving the coil, the stator having an outer yoke which is arranged concentric with the magnet and has an outer circumferential edge extendedly branched at the same interval to form first pole teeth which are opposedly arranged on the outer circumferential face of the magnet with an air gap therefrom, and an inner yoke with one end of smaller diameter being inserted into the inner circumferential face of the coil and the other end of larger diameter extendedly branched while covering the side of the coil to form second pole teeth which are alternately arranged with the first pole teeth.
Preferably, the yoke comprises first and second yokes provided at both axial sides of the magnet.
Preferably, the first and second pole teeth are energized into the polarities different from each other according to the direction of current applied to the coil.
Preferably, the pole teeth of the first yoke and the pole teeth of second yoke are extended toward each other.
Also, preferably, each of the first and second yokes is fixedly inserted into the inner circumferential face of a cylindrical housing.
Preferably, the first and second pole teeth have a proper air gap from each other.
In accordance with another aspect of the invention to obtain the foregoing object, a stepping motor comprises: a cylindrical magnet with a plurality of N-S poles being radially magnetized thereto; a shaft having one end coupled to the center of the magnet and rotationally supported by bearings; a pair of coils wound into the shape of a ring at axial sides of the magnet with air gaps; first and second yokes having an outer yoke shaped as a cylinder for receiving the coils which is arranged concentric with the magnet and has an outer circumferential edge extendedly branched at the same interval to form first pole teeth which are opposedly arranged on the outer circumferential face of the magnet with an air gap therefrom, and an inner yoke with one end of smaller diameter being inserted into the inner circumferential face of the coil and the other end of larger diameter extendedly branched while covering the side of the coil to form second pole teeth which are alternately arranged with the first pole teeth; and a housing for fixedly receiving the outer circumferential edges of the first and second yokes.
Preferably, the first and second pole teeth are energized into the polarities different from each other according to the direction of current applied to the coil.
Also, preferably, the first and second pole teeth have a proper air gap from each other.